“VO2 is both genetic and trainable and varies individually,” said Overton, who worked with the US national team before founding his own coaching business. “It is also affected by altitude, age and gender. The best riders have high VO2s genetically plus are able to push it higher with training. Us mere mortals have VO2s in the 50s, and our VO2 doesn't improve much with training.”

“Research says VO2 is about 80% genetic and the other 20% is trainable,” Overton said. “So if you have a VO2 of 50 off the couch, you probably shouldn't hold your breath for [Team Sky general manager Dave] Brailsford's call."

How much can VO2 be altered by training?

To understand how VO2 can be improved — or not — it helps to understand what oxygen consumption means.

“Think of VO2 Max as a supply-and-demand of oxygen, transporting it from the lungs to working muscles,” said cycling coach Jeff Winkler. “Things that affect that are how well your lungs function at moving oxygen from the air into the blood, the stroke rate and volume of your heart, and capillary density. The demand is the rate that your muscles call for oxygen, a mitochondrial process.”

For untrained people, VO2 Max can be elevated by getting fit. For those who are already fit, VO2 Max gains are much harder to come by.

"An unfit person can improve stroke volume of their heart,” Winkler said. “As they exercise their heart gets bigger, stronger, and you have essentially improved part of the supply chain. You can move more blood and get more oxygen to the muscles. But every person has an innate limit.”

In the blood-doping heyday, EPO raised the VO2 Max of users because it increased the transport capacity of their blood.

For amateur riders new to the sport, cycling coach John Verhuel says people could see 10% gains going from untrained to trained.

“Keep in mind though that body weight is part of the equation, so if you maintain the same ability to process oxygen, but lose some weight, your VO2 Max measurement will increase,” Verheul said. “But there's certainly a genetic ceiling, thus the old #1 rule of success in endurance sports: Pick your parents correctly.”

Should more riders follow Chris Froome and release their physiological test data?

VO2 Max isn’t the sole determiner of cycling success

Power-to-weight ratio is in most cases more crucial than vo2 max, part of the reason why power meters such as this stages unit are so crucial for training:

The measurement of maximal oxygen consumption is only part of the picture in cycling performance. For Tour de France winners like Froome, the key metric is the power-to-weight ratio over various durations, typically expressed as watts per kilogram. (Power-to-drag is also important, particularly in time trials.)

That's because to get up and over the mountains they must be able to sustain that power. It comes down to how long your fire can burn for, not how bright. Further, a high VO2 Max doesn’t necessarily mean high power-to-weight.

“The effort or power output at VO2 Max is something that you can’t sustain; it’s not fully aerobic,” Winkler said. “But as the percentage of your FTP [functional threshold power] creeps up closer to VO2, that’s where the story is. For example, take someone with a VO2 Max of 75 who can only do 60% of that at FTP, versus someone with a VO2 Max of 70 who can do 75%. That latter person will outperform the former consistently.”

Elite riders like Froome possess both extraordinarily high VO2 Max numbers and high aerobically sustainable power outputs. How to improve VO2 max through training

As Winkler illustrates above, just getting fit can improve the VO2 Max for most people as their cardiovascular conditioning improves. Once fit, VO2 Max training gets a lot harder.

“Pretty much any aerobic training, even just riding at zone two [roughly 60-74% of threshold power] will help train VO2 Max,” Verheul said. “Ideally, though, the most effective thing is probably to do intervals at an intensity that elicits VO2 Max. That is to say, go hard enough that your body hits the point where it is processing as much oxygen as it can, and then stay at that point for as much time as possible.”

Verheul recommends the following classic VO2 Max workout:

6 x 5 minutes @110-120% FTP w/ 3-4 minutes recovery

“The limited recovery time means you don't recover completely, and thus get more time at VO2 Max. In that workout, it will generally take about two minutes of the first interval to reach VO2 Max, meaning you're getting three minutes at VO2 Max. But subsequent intervals will only take 90s or less to reach that state, so more of the interval is spent at VO2 Max,” said Verheul, warning that such workouts are hard mentally and physically, and should be done sparingly.

Now, Winkler serves as the head coach of the University of Colorado’s cycling team, as well as a private coach for amateur athletes. In these positions, testing for VO2 Max doesn’t serve much purpose.

“If I was a national team coach, maybe, because a part of my job would be talent identification,” Winkler said. “But my role now, just to make someone better, not really. It could be a number to look at for progression purposes, okay. But in and of itself it doesn’t mean much.”

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